1. Field of the Invention
This invention relates to a control device for a vehicular drive system. The vehicular drive system has an engine, an electrically controlled differential portion and a shifting portion. In the electrically controlled differential portion, with an operating state of an electric motor connected to a rotary element of a differential mechanism for power-transmissive state controlled, a differential state between a rotation speed of an input shaft connected to the engine and a rotation speed of an output shaft is controlled. The shifting portion forms a part of a power-transmitting path between the electrically controlled differential portion and drive wheels. The present invention particularly relates to a technology of a control device for preventing a high-speed rotation of a rotary element of the shifting portion of the differential mechanism.
2. Description of the Related Art
In general, a step-variable type automatic shifting portion is arranged to incorporate therein hydraulically operated frictional engaging devices such as clutches and brakes. Upon appropriately engaging or disengaging these hydraulically operated frictional engaging device, a gear position is established depending on a running state of a vehicle. In addition, a belt-drive type continuously variable shifting portion incorporates therein, for instance, a hydraulic cylinder, disposed inside a pulley, operates to vary a pulley width of the pulley, i.e., a pitch diameter of a steel belt wound on the pulley. This allows the gear position to be controlled at a desired speed ratio, while controlling a clamping force of the steel belt at an appropriate level not to cause a slippage. These hydraulically operated frictional engaging devices and hydraulic cylinder are operated with a supplied hydraulic pressure supplied to the respective devices as a drive source.
In the automatic shifting portion, if a drop occurs in the supplied hydraulic pressure due to some failures in the devices, a drop occurs in torque capacities of the hydraulically operated frictional engaging devices of the automatic shifting portion with a resultant occurrence of slippages. This results in a fear of deterioration occurring in durability of the hydraulically operated frictional engaging devices. In addition, even with the belt-drive type continuously variable shifting portion, if a drop occurs in the supplied hydraulic pressure of the hydraulic cylinder, the clamping force of, for instance, the steel belt decreases, causing a degradation occurring in durability of the steel belt and pulley.
On the contrary, in a shifting controlling device disclosed in Patent Publication 1 (Japanese Patent No. 3044885), a drop occurs in hydraulically operated frictional engaging devices such as clutches or the like, and if shortage of a transfer torque capacity is determined, torque of an engine is decreased. This results in a reduction in torque acting on the hydraulically operated frictional engaging devices, thereby preventing a slippage in excess to minimize deterioration in durability. Further, with a belt-drive type continuously variable transmission disclosed in Patent Publication 2 (Japanese Patent Application Publication No. 1-269620A), an output of an engine is reduced in presence of a failure in hydraulically operated frictional engaging devices of a continuously variable shifting portion. This causes a drop to occur in output to be transferred to a pulley and steel belt to minimize a slippage of the steel belt, thereby preventing degradations of the steel belt and pulley.
The vehicular drive system has one type which includes an engine, an electrically controlled differential portion and a shifting portion forming a part of a power-transmitting path between the electrically controlled differential portion and drive wheels. In the electrically controlled differential portion, with an operating state of an electric motor, connected to a rotary element of a differential mechanism for power-transmissive state controlled, a differential state in rotation speed of an input shaft connected to the engine, and a rotation speed of an output shaft is controlled. Upon selectively engaging hydraulically operated frictional engaging devices such as clutches and brakes or the like, the shifting portion is caused to shift in a proper gear position depending on a running state of a vehicle.
If a drop occurs in the supplied hydraulic pressure (clutch engaging pressure) supplied to the hydraulically operated frictional engaging devices relevant to the shifting operations of the shifting portion due to some failures, a drop occurs in transfer torque capacities of the hydraulically operated frictional engaging devices of the shifting portion, causing the slippage to occur. Then, the rotary elements of the electrically controlled differential portion and the shifting portion increase in high-speed rotations. This results in a fear of deterioration occurring in durability of the rotary elements of the electrically controlled differential portion and the shifting portion.
Further, the drive system incorporates therein an electrically controlled differential portion which is not provided in Patent Publications 1 and 2. Therefore, as the rotary element of the electrically controlled differential portion is subjected to the high-speed rotation, an electric motor connected to such a rotary element, is similarly caused to increase in high-speed rotation, causing a fear of degradation occurring in durability of the electric motor.